In orthogonal frequency multiple access—multiple input multiple output (OFDMA-MIMO) based broadband radio systems such as, but not limited to, those that conform to the institute for electronic and electrical engineers (IEEE) 802.16m or LTE (Long Term Evolution—3GPP 4G technology) systems, beamforming is an effective method to improve the receiving signal to noise ratio (SNR). When the base station's (BS's) transmit antennas are closely mounted, the antenna beam pattern usually has low spatial selectivity, and thus the principle Eigen mode dominates the capacity. In addition, the elements of the ideal precoding vectors are usually constant modulus for highly correlated antennas.
Thus, a strong need exists for techniques using differential precoding for highly correlated channels in wireless networks.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements.